JPH03135081A - Optical amplifier - Google Patents

Abstract

PURPOSE:To acquire an optical amplifier which can acquire a large gain with a low pumping light power by providing a reflecting plate to an optical amplifier projecting end, which has reflection properties to an pumping light wavelength. CONSTITUTION:While pumping light is introduced from an incident end of a fiber amplifier which is doped with erbium, etc., pumping light from an projecting end of the fiber amplifier is reflected and returned again inside the fiber amplifier. In an optical amplification examination of the constitution, light passed through an erbium doped fiber 1 is separated by a dichroic mirror 5 to a signal light 9 of a wavelength of 1.535 mum and attenuated pumping light 8. The pumping light 8 is reflected by a mirror 3 and is made to enter to the erbium doped fiber 1 again. In this case, a power of the pumping light 8 which becomes a part of projection light of the fiber 1 is 25mW. Meanwhile, when it is reflected by the mirror 3 and input to the fiber 1 again, a power of pumping light 7 needed to amplify the signal light 6 by 25dB is 30mW; it can be confirmed that adequate signal light gain can be acquired even with a small power of pumping light.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical amplifier in an optical communication system.

(Prior Art) In recent years, optical communication devices with transmission speeds in the gigabit range have been actively developed as optical communication systems for transmitting large amounts of information. In such optical communication equipment,
Optical amplifiers are expected to bring new developments to optical communication systems. In particular, erbium-doped fiber amplifiers have high gain and low noise, making it possible to improve the reception sensitivity of the intensity modulation direct detection method, and long-distance transmission experiments in the gigabit range have been reported. (For example, “5Gb/s using fiber amplifier, 201km by Hagimoto et al.
Optical Transmission Experiment '1989 Institute of Electronics, Information and Communication Engineers, Autumn National Conference, B-430) In this transmission experiment, the repeater gain was greatly expanded by using a fiber amplifier for the post-amplifier and pre-amplifier, and the effectiveness of the fiber amplifier was It shows gender. This fiber amplifier uses a dichroic mirror at the input end of the erbium-doped fiber to combine an optical signal with a wavelength of 1.535 pm and a pump light with a wavelength of 1.4811 m, and combines the optical signal and pump light with low loss. . In this case, about 50m
We are experimenting with a signal light gain of 30 dB when W pumping light power is input.

(Problems to be Solved by the Invention) As mentioned above, a fiber amplifier can obtain a signal light gain of 30 dB or more, but in order to do so, it requires 50 mW.
A pumping light power of more than 100% is required. It is difficult to achieve a pumping light power of 50 mW or more with current long-wavelength semiconductor lasers, and in the above experimental system, the polarization multiplex circuit and two
Using two semiconductor lasers with a wavelength of 1.4811 m, we are experimenting with high output power by polarization multiplexing the outputs of two semiconductor lasers.

Therefore, this fiber amplifier has a problem in that the configuration of the pumping light section becomes complicated and the reliability and cost of the amplifier decrease. An object of the present invention is to provide an optical amplifier that achieves high gain even with low pumping light power.

(Means for Solving the Problems) The optical amplifier of the present invention includes an optical amplification medium in an optical waveguide, and excites the optical amplification medium with excitation light incident from one input end of the optical waveguide. In an optical amplifier that amplifies signal light that enters and propagates in the optical waveguide,
The present invention is characterized in that a reflection plate having reflection characteristics for the wavelength of the excitation light is provided at the output end of the optical amplifier.

(effect) The present invention will be explained in detail below.

The main feature of the optical amplifier of the present invention is effective use of pumping light. That is, a configuration is adopted in which pumping light is input from the input end of a fiber amplifier doped with erbium or the like, while pumping light exiting from the output end of the fiber amplifier is reflected and returned into the fiber amplifier. Generally, a fiber amplifier is used in a non-saturated region of absorption, but in this case, the utilization efficiency of pumping light is about 50%, and the attenuated pumping light is wasted and emitted from the output end of the fiber amplifier. In the present invention, this attenuated pump light is reflected by a reflecting mirror or the like and returned to the fiber amplifier, thereby improving the utilization efficiency of the pump light from about 50% to about 75%. The aim is to

(Example) Hereinafter, the present invention will be described in detail by showing examples. 1st
1 shows a configuration diagram of an optical amplifier according to a first embodiment of the present invention.

In this embodiment, a semiconductor laser with a wavelength of 1.48 pm was used as the excitation light source 2, and a dichroic mirror 4 was used to combine the signal light 6 with a wavelength of 1.53511 m and the excitation light 7.

Further, as the erbium-doped fiber 1, one with an erbium doping amount of 300 ppm and a length of 25 m is used. In the figure, 10 is an isolator. In this optical amplifier, an optical dichroic mirror 5 that passes through an erbium-doped fiber 1 separates a signal light 9 with a wavelength of 1.535 pm and an attenuated pumping light 8, and the pumping light 8 is reflected by a mirror 3 and then reused. The configuration is such that the light is incident on the erbium-doped fiber 1.

With the above configuration, the wavelength is 1.535 pm and the input power is -30 d.
An optical amplification experiment was conducted for signal light 6 of Bm.

In this experiment, in order to clarify the effect of the present invention, mirror 3
(conventional optical amplifier), and mirror 3
(optical amplifier of the present invention), the optical amplification characteristics were measured. First, when the mirror 3 was removed, the power of the pumping light 7 required to amplify the signal light 6 by 25 dB was 55 mW. At that time, the power of the excitation light 8, which was part of the light emitted from the erbium-doped fiber 1, was 25 mW.

On the other hand, if the mirror 3 is used to reflect the excitation light 8 and input it into the erbium-doped fiber again, the signal light 6 is
The power of pumping light 7 required for 5dB amplification is 30mW.
It was confirmed that sufficient signal light gain could be obtained even if the power of the pumping light was reduced. FIG. 2 shows the configuration of an optical amplifier that is a second embodiment of the present invention. In this embodiment, in consideration of redundancy of the excitation light sources, the first and second excitation light sources 2.14 are semiconductor lasers with a wavelength of 1.48 pm. The excitation lights 15 and 16 from these excitation light sources 2 and 14 have their polarizations orthogonal to each other, and the polarization synthesizer 17
The signals are multiplexed without loss and input into the erbium-doped fiber 1.

The optical filter 13 in FIG. 2 is an optical filter composed of an interference film, and the excitation light 8 with a wavelength of 1.48 pm is reflected.
The signal light 19 having a wavelength of 1.535 pm has a characteristic of being almost transmitted.

The optical amplification characteristics were also measured in the above configuration. the result,
Due to the effect of reexcitation of the excitation light 8 by the optical filter 13,
The power of the pump light 7 to obtain a signal light gain of 25 dB was 28 mW. That is, in this embodiment, sufficient gain can be obtained even if the power of the pumping light 7 is reduced to 28 mW, and the pumping light source 2.14 is made redundant.
High reliability of this optical amplification system can be expected.

Although an optical amplifier using an erbium-doped fiber has been described above, the optical amplifier is not limited to the above example. For example, a semiconductor laser with a wavelength of 0.9811 m may be used as the excitation light source. Furthermore, although a dichroic mirror is used to combine the excitation light and signal light, a fiber coupler or the like in which optical fibers are fused may be used instead. Furthermore, in addition to mirrors and optical filters, a diffraction grating or the like may be used as a reflection plate that reflects the excitation light and makes it enter the erbium-doped fiber again. Further, the wavelength of the signal light is limited to 1.53611 m, and the 1.5511 m band may be used.

In the embodiment, a fiber doped with erbium was used as the fiber amplifier, but a fiber amplifier doped with other rare earth elements may also be used.

(Effects of the Invention) As described above, according to the present invention, an optical amplifier that can obtain a large gain with a small pumping light power can be realized. As a result, the power consumption of the optical amplifier can be reduced, the reliability of the light source can be improved, and the life of the optical amplifier can be extended.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical amplifier according to a first embodiment of the present invention, and FIG. 2 is a block diagram of an optical amplifier according to a second embodiment of the present invention. In the figure 1, erbium-doped fiber, 2.1
4... Excitation light source, 3... Mirror, 4.5... Dichroic mirror, 6.9... Signal light, 7.8.15
．． 16...Excitation light, 10...I-router, 11.
12... Luns, 13... Optical filter, 17... Polarization combiner.

Claims (1)

[Claims] In an optical amplifier that includes an optical amplification medium in an optical waveguide and amplifies signal light that enters and propagates into the optical waveguide by exciting the optical amplification medium with a pumping destination that enters from one input end of the optical waveguide, An optical amplifier characterized in that a reflection plate having reflection characteristics for the wavelength of the excitation light is provided at the output end of the optical amplifier.